Carburetor with check valve bypass

ABSTRACT

A diaphragm-controlled carburetor having a main jet leading from a fuel chamber above the diaphragm to a mixing passage and including a unidirectional check valve allowing flow through a main jet passage from said chamber and a bypass passageway around said check valve for allowing flow of fuel from said main jet passage to said diaphragm to compensate for the inertial effect of an air intake silencer used on said carburetor.

United States Patent [191 Tuckey [11] 3,843,755 [451 Oct. 22, 1974 CARBURETOR WITH CHECK VALVE BYPASS [75] inventor: Charles H. Tuckey, Cass City, Mich.

[73] Assignee: Walbro Corporation, Cass City,

Mich.

[22] Filed: Mar. 29, 1973 [21] Appl. No: 345,841

[52] I US. Cl. 261/69 A, 261/D1G. 68 [51] Int. Cl. F02m 17/04 [58] Field of Search 261/D1G. 68, 69 A [56] References Cited UNITED STATES PATENTS 5/1965 Brown et a]. 26l/DlG. 68 2/1966 Martin et 261/DlG. 68

CHOKE /241 63 11,

III

Meininger t. 261/D1G. 68 Donovan 26l/DlG. 68

1 Primary Examiner-Tim R. Miles Attorney, Agent, or Firm-Barnes, Kisselle, Raisch & Choate 5 7 ABSTRACT A diaphragm-controlled carburetor having a main jet leading from a fuel chamber above the diaphragm to a mixing passage and including a unidirectional check valve allowing flow through a main jet passage from i said chamber and a bypass passageway around said check valve for allowing flow of fuel from said main jet passage to said diaphragm to compensate for the inertial effect of an air intake silencer used on said carburetor.

1 Claim, 2 Drawing Figures CARBURETOR WITH CHECK VALVE BYPASS This invention relates to a Carburetor with Check Valve Bypass and more particularly to a carburetor designed for use with an air intake silencer. The carburetor to be disclosed is fully described in my copending application, entitled Diaphragm Carburetor, Ser. No. 106,178, filed Jan. 13, 1971, now U.S.'Pat. No. 3,738,623, issued June 12, 1973.

A problem in connection with the use of carburetors, particularly on snowmobile engines, has been the noise that is created by the air intake passage. This has been subdued by the use of what are called air intake silencers. One of these silencers is disclosed in my copending application, entitled Air Intake Silencer for Internal Combustion Engines, Ser. No. 318,892, filed Dec. 27, 1972.

The use of these air silencers has been found to affect the operation of a carburetor. It is believed that this is caused by the inertia effect of the air flow in the air intake tube which may be somewhat in the nature of 16 inches in length terminating in a plenum chamber. The effect of this addition to the internal combustion engines having a two-cycle operation has been to increase the vacuum pulse particularly at lower throttle levels when the engine may be lugging down under load. Accordingly, during the intake pulse, the pressure drop is greater and this has a tendency to pull more fuel out of the nozzle. This can have a deleterious effect on the carburetor action in that there is a tendency for the air moving through the carburetor to pull more fuel out of the nozzle than is desirable.

It has been found that this tendency can becorrected by allowing some of the fuel in the main jet above the retaining check valve to drain back into the diaphragm chamber through a check valve bypass opening during the time between each intake pulse.

It is, therefore, an object of the present invention to provide a carburetor which can be readily adapted for use with an air intake silencer on an engine.

Other objects and features of the invention relating to detailsof construction and operation will be apparent inthe. following description and claims in which the principles of operation of the invention are set forth together with the best mode presently contemplated.

Drawings accompany the disclosure and the various views thereof may be briefly described as:

FIG. 1, a sectional view of a diaphragm carburetor having a fuel pump and a vapor pump incorporated therein.

FIG. 2, a plan'view of a diaphragm control plate.

Referring to FIG. 1, a main carburetor housing 120 has a mixing passage 122 with a choke valve 124 and a throttle valve 126. A main fuel passage 130 controlled by a needle valve 132 leads to a fuel well 134 which is connected to a tube 136a leading upwardly through the venturi portion of the mixing passage. The tubehas multiple outlets 138a for fuel. The well 134 also has an air inlet 136 and a feed port 138 leading to an intermediate fuel supply chamber 140 with suitable fuel passages 142. An idle recess 144 has some inter.- mediate passages 146 connecting to the mixing passage and also a main idle port 148 controlled by a needle valve 150.

In the bottom of the housing 120 is formed a diaphragm chamber 160 closed by a diaphragm 162 which acts on one end of a lever l64.pivoted in the housing and carrying at its other end a fuel inlet valve 166 operating in a suitable seat thimble 168 which has a top port opening to arecess 170. A small flexible member 172 provides an anti-back bleed check valve 174 for the entrance of fuel into the main fuel passage and this member also has a small port 176 which furnishes fuel from the diaphragm chamber to the'idle recess 144. The diaphragm 162 is held in place by a first intermediate plate 178 which has a top recess 180 below diaphragm 162 and a bottom recess 182 which serves as a part of a pumping chamber above a diaphragm 184 which is controlled in its motion by a leaf spring member having a pan support portion 186 with a side extension anchoring portion 188 provided with locating tabs 190 clamped against the bottomof the housing 178 by a second intermediate housing plate 192. The pumping chamber 189 is defined by the diaphragm 184 and the shallow opening below it in plate 192.

The spring or plate 186 and the side extension 188 have sufficient resiliency to allow the pan portion 186 overlying diaphragm 184, FIG. 2, tofluctuate up an down in conjunction with the diaphragm 184.

The pan-type spring 184-186 has an important function in the operation of the carburetor. It lies on the pulse exposed side of the diaphragm and is subject alternately to pulses and vacuum from the crankcase of an engine. In a two-cycle engine the vacuum pulses are much stronger than the pressure'pulses. In the operation of the pump, the vacuum pulse will draw fuel into the chamber and the spring isintended to assist the pressure pulse to return the diaphragm in the pump-out portion of the cycle. It has been found that the pan-type spring shown in FIGS. 1 and 2 assists the weak pressure pulse at low throttleor idle conditions. On the other hand, when at wide open throttle when vacuum pulses are weaker, the pan-type spring does not hinder the vacuum action, that is, it does not subtract from the weaker vacuum pulses. The shape of the spring also gives support to the diaphragm, the edges being panned to prevent cutting intothe flexible portion thereof. Accordingly, the pump performs well at the low end idle and, in contrast to the coil spring, does not de tract from operation at the high end full throttle. The diaphragm member .184 also has a valve flap 196 backed by a suitable coil spring to' control a passage which will be described below.

At the left-hand portion of the assembly, as shown in FIG. 1, a pump diaphragm 200 is provided between recesses in plate 178 and a second intermediate plate 192, this being a secondary vapor pump which has a disc-like inlet valve 202 and a flap-type outlet valve 204. The diaphragms 184 and 200 :are pulsed by engine pulses through a connection conduit 206 leading from a crankcase connection of an internal combustion engine to the chamber 182 and thence to a connecting passage 208 to the diaphragm 200.

The bottom side of the intermediate plate 192 has two flat surface recesses 210 and 212' which serve as portions of booster chambers in conjunction with op- A filter screen 232 serves to filter fuel entering the chamber 226 before it passes through the valve 224. The normal flow of fuel for the carburetor system will originate at the tank T and flow through the passage 230 and the filter 232 to the valve 224 in response to fluctuation of the fuel pump diaphragm 184. Fuel will thenflow through passagesleading to the valve 196 to an upwardly extending passage 240 terminating at the recess 170 at the top of the fuel inlet valve. Fuel will then move through the fuel inlet valve 166 in response to control of the lever 164 and the diaphragm 162 so that it is available to the main jet through the one-way valve 174 and also to the intermediate flow chamber 140 and the idle chamber 144. Fuel will thus be available to the mixing chamber as it is called for by reason of the adjustment of the choke and throttle.

The pulse chambers formed by the respectively shallow pockets 210-214 and 212-216 serve to enhance the flow of fuel. It will be noted that chambers 214 and 212 are connected to atmosphere. Chamber 210 is connected to the fuel passage 240 and the chamber 216 is connected to the fuel recess 226.

The vapor removal system of the carburetor is under the control of the pump diaphragm 200 and its respective valves 202 and 204. The inlet valve 202 is connected through a passage 242 which leads to the diaphragm chamber 160 directly adjacent the valve 166 which is a high point in the fuel reservoir above the diaphragm. Thus, any vapor and foam which is created in the diaphragm chamber by reason of the flow of the fuel and the vibration of the carburetor will be pulled through the inlet valve 202 and pushed to the outlet valve 204 which leads to a down passage 244 through the plates 192, 220, and the bottom plate 250 which has formed therein an outlet 252 which will be connected to a fuel tank T. Thus, the out-flow of the vapor pump to passage 244 will carry vapor from the top of diaphragm chamber 160 to the tank. This permits the diaphragm 162 and the related inlet valve 166 to control liquid fuel only and prevents a vapor 'build-up which interferes with the control system built for handling liquid fuel.

It will be noted that since the pump 200 is actuated by pressure pulsations from the engine, it pumps most vigorously at part or idle throttle conditions when the crankcase pulses are longer and stronger. Since this is the time that the least fuel is being pulled through the carburetor and also the least cooling is being accomplished in the engine cavity, the heat build-up at the carburetor location is apt to be greatest. This contributes to the vaporization conditions. Thus, the pump 200 is most effective when most needed.

In order to adapt the carburetor for use with a snowmobile engine, for example, utilizing an air intake silencer, I have provided a bypass opening 260 just to the left of the check valve 174. This bypass opening is not controlled by the check valve 174 and, accordingly, will allow fuel to flow back from the passage into the diaphragm chamber 160. This opening 260 can be readily calibrated in correlation with the intensity of the pulses in the mixing passage so that some of the fuel that would normally be retained in the main fuel jet passages will be drained back into the carburetor diaphragm chamber. This reduces to some degree what might be called the pumping action of the air intake flow and makes it possible to use the carburetor with an air intake silencer while maintaining the efficiency of the carburation. The main flow into the main jet passage will still be through the opening which is controlled by the valve 174 and the bypass passage 260 is primarily for a drain back flow as above described.

I claim:

1. In a carburetor having a diaphragm control fuel inlet valve leading to a diaphragm chamber in which there is a fuel chamber above the diaphragm from which fuel is fed to a mixing passage through a manually regulated orifice to a main jet passage and through supplemental jet passages for idling, that improvement which comprises, in combination:

a. a check valve independent of the diaphragm leading from said fuel chamber to said main jet passage for unidirectional flow from said chamber to said passage, and v b. a means forming a bypass passageway independent of said manually regulated orifice and around said check valve to connect said fuel chamber to said main jet passage, said passageway being calibrated to allow fuel to return directly from said main jet passage to said fuel chamber when said check valve is closed. 

1. In a carburetor having a diaphragm control fuel inlet valve leading to a diaphragm chamber in which there is a fuel chamber above the diaphragm from which fuel is fed to a mixing passage through a manually regulated orifice to a main jet passage and through supplemental jet passages for idling, that improvement Which comprises, in combination: a. a check valve independent of the diaphragm leading from said fuel chamber to said main jet passage for unidirectional flow from said chamber to said passage, and b. a means forming a bypass passageway independent of said manually regulated orifice and around said check valve to connect said fuel chamber to said main jet passage, said passageway being calibrated to allow fuel to return directly from said main jet passage to said fuel chamber when said check valve is closed. 